Polymer dosing, in this instance was complicated by the saline nature of the river water in the pipe. To determine the correct polymer type and dosing concentration a representative sample of dredge slurry was sent to the Geofabrics Center of Excellence Laboratory for analysis, and a specialist polymer supplier with the capability to provide dosing equipment engaged to assist with this element of the work. To ensure rapid and effective dewatering it was necessary to dose sediments with a polymer flocculant. The quality of liquids discharged from the tube had to be controlled and meet environmental requirements in order to be allowed to flow back into the river. Sediment excavated by the remotely controlled dredger would be pumped into the Geotube® dewatering units and dewatered on the barge which would then be towed downriver to a location where the dewatered sediments could be excavated and disposed. Prefabricated concrete submerged structures appear to be reasonable alternatives.
#Submerge breakwater geotube how to
The challenge faced by the specialist contractor was how to contain sludge excavated from a blocked stormwater pipe by a remote-controlled underwater dredger operating in constricted conditions in a location highly visible to the public and required to meet stringent environmental and operating mandates.Ĭhallenges ranging from identifying a method of containing and dewatering dredged sediments and applying a suitable polymer flocculant in a saline water environment to sediments that varied from fine contaminated clay to residual sand deposits as well as avoiding all risk of accidental discharge of contaminated sediments into the river had to be addressed before work could proceed.įollowing discussions of the challenges faced by Desilting Solutions, a contractor specializing in remote underwater dredging it was proposed to place two GT500D Geotube® dewatering units 30.6m in length laid adjacent to each other on a barge moored next to another barge controlling the remote dredging equipment. The submerged location of the outfall of the pipe required the dewatering be conducted from barges moored in the Brisbane river. This technically difficult project required a variety of innovative solutions to meet operational and environmental requirements. Exhumed sediments were pumped into Geotube® dewatering units placed on a barge moored in the river. This becomes an attractive proposition where rock is expensive and difficult to obtain and where the water forces are not extreme.In a first of its kind application in Australia a specially designed remote-controlled underwater dredger was deployed to excavate and clean out a blocked stormwater drain discharging into the Brisbane river. This fascine mattress can then be ballasted into position on the seabed by dropping rocks onto the floating fascine mattress as it sinks.Ī better alternative to rock is the Geotube® and Geocontainer® systems which are effective methods of replacing the rock-fill core of breakwaters. To facilitate easy installation of this filter, Mirafi® FM is fabricated into a fascine mattress which can be floated out to sea and sunk into place. To prevent this, a Mirafi® FM woven geotextile is installed across the top of the sand foundation prior to the construction of the breakwater to act as a filter in preventing the erosion of the sand foundation through the breakwater. If the breakwater is founded on sand, this can result in severe sand erosion and consequent breakwater instability. In dissipating wave energy considerable turbulence can occur at the toe and across the base of breakwaters. Detached breakwaters are sometimes designed to permanents submerged and may be designed to retain a perched or artificial beach behind. Breakwaters may be attached to, or detached from, the shoreline. Consequently, the water conditions on the protected side of the breakwater remain relatively calm. Breakwaters reduce the wave energy by partial reflection as well as by breaking on the structure. Breakwaters are marine structures that reduce water forces offshore before they reach land thus preventing erosion.
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